package com.yuanfeng.commoms.util;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.encoders.Base64;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.Key;
import java.security.Security;

public class WechatDecryptDataUtil {
	 public static void main(String[] args) {
	        String result = decryptData(
	                "tkr8ytjqb8MYL0zznRbWugMQlaLDfVRoeOFHsz8p/H/Jg+HeDVDzoEojQAYz0+XgQWkFYO48X4k5xlHJvUBp5glGCloemMmwJfKIKKxtzBTimbzc+rXJzoQXCMZDjsVZapvxNYmcMH7SdAyj484TcIMluMMvVoNypeKf7Wk8/1EsiiTP5NQqR6GTcRYn9nuT1WF6mL2FlvH6bV9bP3XK/w==",
	                "w+jH2pXeXJr7+2enUBHx2Q==",
	                "ykMD+HWcTndgyPgiq7CULQ=="
	        );
	        System.out.println("result = " + result);
	    }

	    public static String decryptData(String encryptDataB64, String sessionKeyB64, String ivB64) {
	        return new String(
	                decryptOfDiyIV(
	                        Base64.decode(encryptDataB64),
	                        Base64.decode(sessionKeyB64),
	                        Base64.decode(ivB64)
	                )
	        );
	    }

	    private static final String KEY_ALGORITHM = "AES";
	    private static final String ALGORITHM_STR = "AES/CBC/PKCS7Padding";
	    private static Key key;
	    private static Cipher cipher;

	    private static void init(byte[] keyBytes) {
	        // 如果密钥不足16位，那么就补足.  这个if 中的内容很重要
	        int base = 16;
	        if (keyBytes.length % base != 0) {
	            int groups = keyBytes.length / base + (keyBytes.length % base != 0 ? 1 : 0);
	            byte[] temp = new byte[groups * base];
	            Arrays.fill(temp, (byte) 0);
	            System.arraycopy(keyBytes, 0, temp, 0, keyBytes.length);
	            keyBytes = temp;
	        }
	        // 初始化
	        Security.addProvider(new BouncyCastleProvider());
	        // 转化成JAVA的密钥格式
	        key = new SecretKeySpec(keyBytes, KEY_ALGORITHM);
	        try {
	            // 初始化cipher
	            cipher = Cipher.getInstance(ALGORITHM_STR, "BC");
	        } catch (Exception e) {
	            e.printStackTrace();
	        }
	    }

	    /**
	     * 解密方法
	     *
	     * @param encryptedData 要解密的字符串
	     * @param keyBytes      解密密钥
	     * @param ivs           自定义对称解密算法初始向量 iv
	     * @return 解密后的字节数组
	     */
	    private static byte[] decryptOfDiyIV(byte[] encryptedData, byte[] keyBytes, byte[] ivs) {
	        byte[] encryptedText = null;
	        init(keyBytes);
	        try {
	            cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(ivs));
	            encryptedText = cipher.doFinal(encryptedData);
	        } catch (Exception e) {
	            e.printStackTrace();
	        }
	        return encryptedText;
	    }
}
